Tag Archives: fn 5.7 ar upper

By David Crane defrev at gmail dot com August 11, 2008 An outfit called 57 Center is making an interesting patent-pending 5.7x28mm upper receiver for AR-15/M16 lower receivers called the AR Five Seven (AR-57) that utilizes 50-round FN P90/PS90 PDW magazines. The magazines are top-loaded and horizontal-mounted, just like on the P90/PS90. It would appear that that an emptied-out standard ... Read More »